Different bioselective voltammetric electrodes will be developed as effective sensors for pharmaceutical and clinically important compounds in body fluids. Enhanced selectivity and sensitivity will be achieved by controlled accumulation of the desired compound (or group of compounds) onto the electrode surface. This preconcentration step will be accomplished by selective attachment (via covalent reaction) or preferential adsorption to surfaces of modified or ordinary electrodes. Electrode coverage, with a proper membrane or polymer, would provide additional selectivity by controlling the access to the surface. Following the controlled preconcentration step, the electrode will be transferred from the sample solution to a suitable blank solution where the surface-bound species will be quantified. Such 'medium exchange' procedure will enhance the selectivity by eliminating background currents due to solution-phase species. Large array of drugs, vitamins, toxic organic compounds and other compounds of clinical importance will be tested as candidates for this bioselective voltammetric detection. In order to realize the best possible response for each analyte (high specificity and minimum matrix interferences), we will examine various experimental conditions, such as electrode material and functionalities, solution composition, pH, temperature, mass-transport or membrane porosity. Various surface modification procedures will be examined for obtaining the specific response. The optimum combination of these operating conditions will be used in the operation of the designed dipping-type clinical sensors. Competition experiments will be designed to test the specificity of the sensor. Applications to selective measurements of various drugs, biochemical and carcinogens in body fluids, using batch and flow systems will be tested and demonstrated.